Alteration in articular cartilage in subtalar coalition: A comparative analysis

Subtalar coalition (SC) is a rare pathological connection between the talus and calcaneum. SC can be osseous, fibrous, or cartilaginous forms, with the type of coalition affecting symptoms and management. Although the impact of osseous coalition has been studied, the subtalar joint's articular cartilage thickness remains inadequately explored across patients with osseous, fibrous subtalar coalition and those without coalition. Cartilage thinning is of particular clinical importance as it may represent early degenerative change and influence surgical decision-making. This study aimed to analyse and compare articular cartilage thickness between these patient groups.

We conducted a retrospective study using our Computerized Radiology Information System, searching with the keyword 'subtalar coalition'. Utilising our Picture Archive and communication system, we measured articular cartilage thickness of the posterior facet of the subtalar joint (PFSJ) on foot and ankle MRI and CT scans for patients with normal joints, osseous coalition, and fibrous coalition. Statistical analyses were performed using ANOVA with a significance threshold set at p < 0.05.

In the anterior 1/3 region of the PFSJ, articular cartilage thickness measurement was higher in fibrous subtalar coalition (2.3 mm) in comparison to normal (1.7 mm) and bony subtalar coalition (1.4 mm). Similar results were noted in middle 1/3 region, posterior 1/3, medial, and lateral 1/3 too. Across all measured regions, osseous subtalar coalition demonstrated relative cartilage thinning compared to both fibrous coalition and normal joints.

Our study showed that there is relative hypertrophy of articular cartilage in fibrous subtalar coalition. Importantly, osseous subtalar coalition is associated with relative cartilage thinning, which may represent reduced joint loading and a potential precursor to osteoarthritis. This finding is likely to be more clinically relevant when considering management options, as preserved or hypertrophic cartilage may support excision, whereas cartilage thinning may favour fusion. These findings can have potentially affecting treatment decisions and patient care.

There is relative hypertrophy of articular cartilage in fibrous subtalar coalition.